The burning of biomass in the form of construction and demolition wood residue and wood generated from logging and pest control activities has been a substantial increase over the past several years. As the cost of fossil fuels (e.g. fuel oil, bunker oil, and natural gas) has increased, many large-scale users of these fossil fuels have looked to biomass as an alternative to provide a cost-effective fuel to supply their energy needs.
Large scale commercial greenhouses in particular have been on the forefront of the conversion to biomass fuel as a replacement for natural gas and bunker oil which have historically been used to generate hot water which in turn is used to provide heat to their greenhouses during the seasonal heating season. Primary sources of biomass used in the greenhouse industry are organic materials such as construction and demolition wood waste, clean wood, farm waste such as tomato vines, yard waste from trees, grass clippings and bushes, furniture and green wood generated from the removal of trees.
Additionally, recent interest has been expressed in the development of small to midsize electrical generation plants which would use wood waste from logging operations to provide steam for the operation of the facility's steam turbines.
While the conversion of large scale heating systems in electrical generating facilities to biomass as a fuel is primarily driven by cost savings realized from using biomass versus fossil fuels, there are also significant environmental benefits to this conversion. Biomass is typically seen as a carbon-neutral fuel while fossil fuels are significant contributors to global warming through the release of greenhouse gases.
Many large scale energy users have already made the conversion to biomass fuel in the form of residual wood. However, these conversions have typically been made without adequate research, and problems associated with the conversion process have resulted in the project owner not fully realizing the cost savings in environmental benefits that are anticipated to result from the conversion. The major problems encountered include the ability to source “dry wood” as a biomass fuel supply, inappropriately designed combustion units, and inefficient pollution control equipment to control emissions from biomass combustion.
Wood removed under this program is chipped and used in biomass burners without adequate seasoning to allow the wood to dry out. Green wood has a moisture content of up to 80% while seasoned wood has a moisture content of between 20-25%. Burning of green wood results in a significantly reduced energy of the biomass burner which in turn results in fouling of the combustion unit from creosote buildup and increased atmosphere pollution associated with the burning of biomass. Accordingly, it would be advantageous to develop an air emissions control method and apparatus to be used in connection with a biomass dryer/burner system for drying and burning green wood.
A previously known air filtration system for a biomass dryer/burners is known as a bag system. A bag system is comprised of a plurality of filters, each filter operable to remove particles from dry air. Previously known bag systems are not capable of cleaning moist air, or an air/water mixture. Bag systems are only capable of filtering emissions from a biomass dryer/burner system emitting dry air emissions.
While the conversion from fossil fuels to biomass often results in cost savings and environmental benefits, the environmental benefits are not realized unless the emissions from the biomass burner are neutralized to government air emission standards. Accordingly, it would be advantageous to develop an air emissions control method and apparatus to be used in connection with a biomass dryer/burner system which enables the scrubbing of an air/water mixture.